Oxide semiconductor device with oxide semiconductor layers of different oxygen concentrations and method of manufacturing the same
A phenomenon of change of a contact resistance between an oxide semiconductor and a metal depending on an oxygen content ratio in introduced gas upon depositing an oxide semiconductor film made of indium gallium zinc oxide, zinc tin oxide, or others in an oxide semiconductor thin-film transistor. A contact layer is formed with an oxygen content ratio of 10% or higher in a region from a surface, where the metal and the oxide semiconductor are contacted, down to at least 3 nm deep in depth direction, and a region to be a main channel layer is further formed with an oxygen content ratio of 10% or lower, so that a multilayered structure is formed, and both of ohmic characteristics to the electrode metal and reliability such as the suppression of threshold potential shift are achieved.
1. An oxide semiconductor device comprising an oxide semiconductor layer and first and second electrodes contacting a first surface of the oxide semiconductor layer,
wherein the oxide semiconductor layer includes:
a first layer having a substantially uniform first oxygen-content concentration; and
a second layer provided between the first and second electrodes and the first layer such that an upper surface of the second layer contacts bottom surfaces of the first and second electrodes, and having a substantially uniform second oxygen-content concentration, and
wherein the second oxygen-content concentration is higher than the first oxygen-content concentration.
2. The oxide semiconductor device according to claim 1 , wherein
the second layer has a thickness of 3 nm or larger.
3. The oxide semiconductor device according to claim 1 , wherein
the second oxygen-content concentration is 10 21 atomic concentration or higher, and
the first oxygen-content concentration is below 10 21 atomic concentration.
4. The oxide semiconductor device according to claim 1 , wherein
there is a 10 times or more difference between the first oxygen-content concentration and the second oxygen-content concentration.
5. The oxide semiconductor device according to claim 1 , wherein
the oxide semiconductor layer includes one of zinc oxide (ZnO), indium gallium zinc oxide (IGZO), zinc tin oxide (ZTO), and zinc indium oxide (ZIO).
6. The oxide semiconductor device according to claim 1 , wherein
a third layer, in which a difference in the oxygen concentrations relative to the first layer and the second layer is gradedly decreased, is provided between the first layer and the second layer.
7. The oxide semiconductor device according to claim 1 , wherein
a layer having a substantially uniform oxygen-content concentration within a range of the oxygen-content concentration of the first layer and the oxygen-content concentration of the second layer is provided between the first layer and the second layer.
8. The oxide semiconductor device according to claim 1 , wherein
each of the first and second electrodes comprises a plurality of layers including a transparent conductive film contacting the oxide semiconductor layer, the transparent conductive film having a lower conductivity than a conductivity of a second layer of the first and second electrodes not contacting the oxide semiconductor layer.
9. The oxide semiconductor device according to claim 1 , wherein
a transistor of a bottom-gate top-contact type or a top-gate bottom-contact type is configured having:
a gate electrode provided on a second surface of the oxide semiconductor layer with an interposing gate insulating film; and
a source electrode and a drain electrode contacting the first surface of the oxide semiconductor layer.
10. An active matrix substrate including the oxide semiconductor device according to claim 9 , wherein
a plurality of gate lines and a plurality of data lines are provided on a substrate, and
a transistor as aforesaid is arranged in each pixel arranged in the matrix at intersections of the plurality of gate lines and the plurality of data lines.
11. The oxide semiconductor device according to claim 1 , wherein
a transistor of a top-gate top-contact type or a bottom-gate bottom-contact type is configured having:
a gate electrode provided on a second surface of the oxide semiconductor layer with an interposing gate insulating film; and
a source electrode and a drain electrode contacting the first surface of the oxide semiconductor layer.
12. An active matrix substrate including the oxide semiconductor device according to claim 11 , wherein
a plurality of gate lines and a plurality of data lines are provided on a substrate, and
a transistor as aforesaid is arranged in each pixel arranged in the matrix at intersections of the plurality of gate lines and the plurality of data lines.